This invention relates to a process for the production of gaseous streams comprising H.sub.2 and CO e.g. synthesis gas, reducing gas, and fuel gas by the partial oxidation of solid carbonaceous fuels. More specifically, it pertains to a process for feeding particulate solid carbonaceous fuel to a partial oxidation gas generator operating at high pressure.
The partial oxidation of solid carbonaceous fuels, such as coal or petroleum coke represents a well-known, highly economical method for the production of large quantities of gaseous mixtures comprising H.sub.2, CO, CO.sub.2, H.sub.2 O, CH.sub.4, N.sub.2, COS, and H.sub.2 S. The solid fuel may be introduced into the free-flow reaction chamber as a dispersion or suspension of pulverized or particulate solid carbonaceous fuel in a gaseous or liquid carrier.
In coassigned U.S. Pat. Nos. 2,595,234- Eastman; 2,946,670- Whaley; 2,987,387- Carkeek et al; and 3,544,291 -Schlinger et al, the solid fuel in particle form is mixed with water to form a slurry or suspension of the solid particles. The suspension is passed through a tubular heating zone, for example, an externally heated helical coil, wherein it is heated and substantially all of the water is converted into steam. A dispersion of solid fuel particles in steam is formed in the heating step and is then introduced into the reaction zone. One disadvantage of the prior art process is the difficulty in maintaining the slurry heaters which are subject to scale formation on the inner surface of the heater tubes and erosion from the solid particles. Further, should excess H.sub.2 O be introduced into the reaction zone, the efficiency of the process is reduced. The process of the present invention avoids these problems by obviating the necessity for the use boilers or heaters for the coal-water slurry feed to the gas generator. Further, there is better control of the amount of H.sub.2 O that enters the reaction zone of the partial oxidation gas generator.
Substantially all or a portion of the steam from the aforesaid dispersion may be removed by means of a vortex chamber or cyclone separation as provided in coassigned Carkeek et al U.S. Pat. Nos. 2,829,957; 2,864,156; and 2,987,387. This step is also present in U.S. Pat. No. 3,871,839- Moody, and U.S. Pat. No. 4,153,427- Bissett et al. While the previous steam skimming feed systems offer some potential advantage in enhancing gasification efficiency, a major problem with them is encountered in designing the necessary slurry vaporizers. This is due to lack of knowledge of the heat transfer coefficients and processes associated with slurry vaporization, difficulties with control aspects, coking, plugging, and fouling problems. These problems have been avoided by the subject process. It was unexpectedly found in the subject process that by direct injection of superheated steam into the slurry lines to vaporize the slurry, the solid carbonaceous fuel may undergo thermal beneficiation producing a CO.sub.2 -containing by-product gas stream. Using direct injection of superheated steam to vaporize the slurry has a number of other advantages over the use of prior art skimming systems, steam exchangers of fire heaters. Some of these other advantages follow:
1. By using direct injection into the pipeline carrying the aqueous slurry of particulate solid carbonaceous fuel, it becomes much simpler to control the vaporization process since known quantities of steam are added at particular locations. PA0 2. Problems with fouling or char formation are avoided. PA0 3. Designs are simplified over those of heat exchangers and entrained bed dryers since it becomes much simpler to predict vapor and bulk velocities in the system.